Participants may choose to enter an observational period at any time before they start Step 2 or Step 3. During the observational period, participants continue to take HAART but not VPA or enfuvirtide. Upon entering an observational period, study staff will contact the participant every 8 weeks for a review of their medical records. Each participant will have a study visit within 8 weeks of beginning a new step. These interim study screenings include a physical exam, medical history, and blood and urine collection. Participants may be asked to have additional leukapheresis performed if they have discontinued study medications for 12 weeks or more.